1. Field of the invention
The present invention relates to a motor-driven shutter for use in a camera with automatic focusing and exposure control.
2. Description of the Prior Art
Japanese Laid-Open Patent Publication No. 61-9631 discloses a shutter which, in combination with a single stepping motor is capable of continuously effecting a focusing operation, exposing operation an according to the brightness an object to be photographed, and a returning operation. According to the disclosed shutter device, a range adjustment lever which is biased by a spring is held in abutment against a drive lever that is arrested and driven by the stepping motor, and the range adjustment lever is engaged in a focused position for thereby setting the objective lens in the focused position.
With this arrangement, the resilient force of the spring acting on the range adjustment lever is applied via the drive lever to the stepping motor When the stepping motor is not in use, the motor has to hold the drive lever and other members in a standby position while resisting the spring force under the magnetic coupling force of the rotor and stator of the motor. In the event that the camera is subjected to a shock, the spring force and the magnetic coupling force are brought out of balance, shifting the stator and the rotor out of phase with each other, so that the shutter will not operate properly.